| Abstract | A survey of 41 radio galaxies for H I absorption was made. One new absorption system was found, that in 3C 178. Upper limits to the H I optical depth are derived for the remaining systems. The observations extend to z = 0.34, corresponding to the low-frequency limit of the receiver. The absorption data indicate that, for an optical depth of 0.03 or less, the product of the spatial density of H I clouds and their projected area is less than 0.0022 per Mpc. Although this product is not particularly restrictive, it does indicate a discrete cloud H I mass-density model at least an order of magnitude less than the critical cosmological density. Some emission data supply an upper bound on the spatial density of H I clouds of mass above approximately one billion solar masses. |
